/*
 * Copyright (c) 1996, 2011, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.rmi.server;

import java.rmi.Remote;
import java.rmi.NoSuchObjectException;
import java.lang.reflect.Proxy;
import sun.rmi.server.Util;

/**
 * The <code>RemoteObject</code> class implements the
 * <code>java.lang.Object</code> behavior for remote objects.
 * <code>RemoteObject</code> provides the remote semantics of Object by
 * implementing methods for hashCode, equals, and toString.
 *
 * @author Ann Wollrath
 * @author Laird Dornin
 * @author Peter Jones
 * @since JDK1.1
 */
public abstract class RemoteObject implements Remote, java.io.Serializable {

  /**
   * The object's remote reference.
   */
  transient protected RemoteRef ref;

  /**
   * indicate compatibility with JDK 1.1.x version of class
   */
  private static final long serialVersionUID = -3215090123894869218L;

  /**
   * Creates a remote object.
   */
  protected RemoteObject() {
    ref = null;
  }

  /**
   * Creates a remote object, initialized with the specified remote
   * reference.
   *
   * @param newref remote reference
   */
  protected RemoteObject(RemoteRef newref) {
    ref = newref;
  }

  /**
   * Returns the remote reference for the remote object.
   *
   * <p>Note: The object returned from this method may be an instance of
   * an implementation-specific class.  The <code>RemoteObject</code>
   * class ensures serialization portability of its instances' remote
   * references through the behavior of its custom
   * <code>writeObject</code> and <code>readObject</code> methods.  An
   * instance of <code>RemoteRef</code> should not be serialized outside
   * of its <code>RemoteObject</code> wrapper instance or the result may
   * be unportable.
   *
   * @return remote reference for the remote object
   * @since 1.2
   */
  public RemoteRef getRef() {
    return ref;
  }

  /**
   * Returns the stub for the remote object <code>obj</code> passed
   * as a parameter. This operation is only valid <i>after</i>
   * the object has been exported.
   *
   * @param obj the remote object whose stub is needed
   * @return the stub for the remote object, <code>obj</code>.
   * @throws NoSuchObjectException if the stub for the remote object could not be found.
   * @since 1.2
   */
  public static Remote toStub(Remote obj) throws NoSuchObjectException {
    if (obj instanceof RemoteStub ||
        (obj != null &&
            Proxy.isProxyClass(obj.getClass()) &&
            Proxy.getInvocationHandler(obj) instanceof
                RemoteObjectInvocationHandler)) {
      return obj;
    } else {
      return sun.rmi.transport.ObjectTable.getStub(obj);
    }
  }

  /**
   * Returns a hashcode for a remote object.  Two remote object stubs
   * that refer to the same remote object will have the same hash code
   * (in order to support remote objects as keys in hash tables).
   *
   * @see java.util.Hashtable
   */
  public int hashCode() {
    return (ref == null) ? super.hashCode() : ref.remoteHashCode();
  }

  /**
   * Compares two remote objects for equality.
   * Returns a boolean that indicates whether this remote object is
   * equivalent to the specified Object. This method is used when a
   * remote object is stored in a hashtable.
   * If the specified Object is not itself an instance of RemoteObject,
   * then this method delegates by returning the result of invoking the
   * <code>equals</code> method of its parameter with this remote object
   * as the argument.
   *
   * @param obj the Object to compare with
   * @return true if these Objects are equal; false otherwise.
   * @see java.util.Hashtable
   */
  public boolean equals(Object obj) {
    if (obj instanceof RemoteObject) {
      if (ref == null) {
        return obj == this;
      } else {
        return ref.remoteEquals(((RemoteObject) obj).ref);
      }
    } else if (obj != null) {
            /*
             * Fix for 4099660: if object is not an instance of RemoteObject,
             * use the result of its equals method, to support symmetry is a
             * remote object implementation class that does not extend
             * RemoteObject wishes to support equality with its stub objects.
             */
      return obj.equals(this);
    } else {
      return false;
    }
  }

  /**
   * Returns a String that represents the value of this remote object.
   */
  public String toString() {
    String classname = Util.getUnqualifiedName(getClass());
    return (ref == null) ? classname :
        classname + "[" + ref.remoteToString() + "]";
  }

  /**
   * <code>writeObject</code> for custom serialization.
   *
   * <p>This method writes this object's serialized form for this class
   * as follows:
   *
   * <p>The {@link RemoteRef#getRefClass(java.io.ObjectOutput) getRefClass}
   * method is invoked on this object's <code>ref</code> field
   * to obtain its external ref type name.
   * If the value returned by <code>getRefClass</code> was
   * a non-<code>null</code> string of length greater than zero,
   * the <code>writeUTF</code> method is invoked on <code>out</code>
   * with the value returned by <code>getRefClass</code>, and then
   * the <code>writeExternal</code> method is invoked on
   * this object's <code>ref</code> field passing <code>out</code>
   * as the argument; otherwise,
   * the <code>writeUTF</code> method is invoked on <code>out</code>
   * with a zero-length string (<code>""</code>), and then
   * the <code>writeObject</code> method is invoked on <code>out</code>
   * passing this object's <code>ref</code> field as the argument.
   *
   * @serialData The serialized data for this class comprises a string (written with
   * <code>ObjectOutput.writeUTF</code>) that is either the external ref type name of the contained
   * <code>RemoteRef</code> instance (the <code>ref</code> field) or a zero-length string, followed
   * by either the external form of the <code>ref</code> field as written by its
   * <code>writeExternal</code> method if the string was of non-zero length, or the serialized form
   * of the <code>ref</code> field as written by passing it to the serialization stream's
   * <code>writeObject</code> if the string was of zero length.
   *
   * <p>If this object is an instance of {@link RemoteStub} or {@link RemoteObjectInvocationHandler}
   * that was returned from any of the <code>UnicastRemoteObject.exportObject</code> methods and
   * custom socket factories are not used, the external ref type name is <code>"UnicastRef"</code>.
   *
   * If this object is an instance of <code>RemoteStub</code> or <code>RemoteObjectInvocationHandler</code>
   * that was returned from any of the <code>UnicastRemoteObject.exportObject</code> methods and
   * custom socket factories are used, the external ref type name is <code>"UnicastRef2"</code>.
   *
   * If this object is an instance of <code>RemoteStub</code> or <code>RemoteObjectInvocationHandler</code>
   * that was returned from any of the <code>java.rmi.activation.Activatable.exportObject</code>
   * methods, the external ref type name is <code>"ActivatableRef"</code>.
   *
   * If this object is an instance of <code>RemoteStub</code> or <code>RemoteObjectInvocationHandler</code>
   * that was returned from the <code>RemoteObject.toStub</code> method (and the argument passed to
   * <code>toStub</code> was not itself a <code>RemoteStub</code>), the external ref type name is a
   * function of how the remote object passed to <code>toStub</code> was exported, as described
   * above.
   *
   * If this object is an instance of <code>RemoteStub</code> or <code>RemoteObjectInvocationHandler</code>
   * that was originally created via deserialization, the external ref type name is the same as that
   * which was read when this object was deserialized.
   *
   * <p>If this object is an instance of <code>java.rmi.server.UnicastRemoteObject</code> that does
   * not use custom socket factories, the external ref type name is <code>"UnicastServerRef"</code>.
   *
   * If this object is an instance of <code>UnicastRemoteObject</code> that does use custom socket
   * factories, the external ref type name is <code>"UnicastServerRef2"</code>.
   *
   * <p>Following is the data that must be written by the <code>writeExternal</code> method and read
   * by the <code>readExternal</code> method of <code>RemoteRef</code> implementation classes that
   * correspond to the each of the defined external ref type names:
   *
   * <p>For <code>"UnicastRef"</code>:
   *
   * <ul>
   *
   * <li>the hostname of the referenced remote object, written by {@link
   * java.io.ObjectOutput#writeUTF(String)}
   *
   * <li>the port of the referenced remote object, written by {@link java.io.ObjectOutput#writeInt(int)}
   *
   * <li>the data written as a result of calling {link java.rmi.server.ObjID#write(java.io.ObjectOutput)}
   * on the <code>ObjID</code> instance contained in the reference
   *
   * <li>the boolean value <code>false</code>, written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
   *
   * </ul>
   *
   * <p>For <code>"UnicastRef2"</code> with a <code>null</code> client socket factory:
   *
   * <ul>
   *
   * <li>the byte value <code>0x00</code> (indicating <code>null</code> client socket factory),
   * written by {@link java.io.ObjectOutput#writeByte(int)}
   *
   * <li>the hostname of the referenced remote object, written by {@link
   * java.io.ObjectOutput#writeUTF(String)}
   *
   * <li>the port of the referenced remote object, written by {@link java.io.ObjectOutput#writeInt(int)}
   *
   * <li>the data written as a result of calling {link java.rmi.server.ObjID#write(java.io.ObjectOutput)}
   * on the <code>ObjID</code> instance contained in the reference
   *
   * <li>the boolean value <code>false</code>, written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
   *
   * </ul>
   *
   * <p>For <code>"UnicastRef2"</code> with a non-<code>null</code> client socket factory:
   *
   * <ul>
   *
   * <li>the byte value <code>0x01</code> (indicating non-<code>null</code> client socket factory),
   * written by {@link java.io.ObjectOutput#writeByte(int)}
   *
   * <li>the hostname of the referenced remote object, written by {@link
   * java.io.ObjectOutput#writeUTF(String)}
   *
   * <li>the port of the referenced remote object, written by {@link java.io.ObjectOutput#writeInt(int)}
   *
   * <li>a client socket factory (object of type <code>java.rmi.server.RMIClientSocketFactory</code>),
   * written by passing it to an invocation of <code>writeObject</code> on the stream instance
   *
   * <li>the data written as a result of calling {link java.rmi.server.ObjID#write(java.io.ObjectOutput)}
   * on the <code>ObjID</code> instance contained in the reference
   *
   * <li>the boolean value <code>false</code>, written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
   *
   * </ul>
   *
   * <p>For <code>"ActivatableRef"</code> with a <code>null</code> nested remote reference:
   *
   * <ul>
   *
   * <li>an instance of <code>java.rmi.activation.ActivationID</code>, written by passing it to an
   * invocation of <code>writeObject</code> on the stream instance
   *
   * <li>a zero-length string (<code>""</code>), written by {@link java.io.ObjectOutput#writeUTF(String)}
   *
   * </ul>
   *
   * <p>For <code>"ActivatableRef"</code> with a non-<code>null</code> nested remote reference:
   *
   * <ul>
   *
   * <li>an instance of <code>java.rmi.activation.ActivationID</code>, written by passing it to an
   * invocation of <code>writeObject</code> on the stream instance
   *
   * <li>the external ref type name of the nested remote reference, which must be
   * <code>"UnicastRef2"</code>, written by {@link java.io.ObjectOutput#writeUTF(String)}
   *
   * <li>the external form of the nested remote reference, written by invoking its
   * <code>writeExternal</code> method with the stream instance (see the description of the external
   * form for <code>"UnicastRef2"</code> above)
   *
   * </ul>
   *
   * <p>For <code>"UnicastServerRef"</code> and <code>"UnicastServerRef2"</code>, no data is written
   * by the <code>writeExternal</code> method or read by the <code>readExternal</code> method.
   */
  private void writeObject(java.io.ObjectOutputStream out)
      throws java.io.IOException, java.lang.ClassNotFoundException {
    if (ref == null) {
      throw new java.rmi.MarshalException("Invalid remote object");
    } else {
      String refClassName = ref.getRefClass(out);
      if (refClassName == null || refClassName.length() == 0) {
                /*
                 * No reference class name specified, so serialize
                 * remote reference.
                 */
        out.writeUTF("");
        out.writeObject(ref);
      } else {
                /*
                 * Built-in reference class specified, so delegate
                 * to reference to write out its external form.
                 */
        out.writeUTF(refClassName);
        ref.writeExternal(out);
      }
    }
  }

  /**
   * <code>readObject</code> for custom serialization.
   *
   * <p>This method reads this object's serialized form for this class
   * as follows:
   *
   * <p>The <code>readUTF</code> method is invoked on <code>in</code>
   * to read the external ref type name for the <code>RemoteRef</code>
   * instance to be filled in to this object's <code>ref</code> field.
   * If the string returned by <code>readUTF</code> has length zero,
   * the <code>readObject</code> method is invoked on <code>in</code>,
   * and than the value returned by <code>readObject</code> is cast to
   * <code>RemoteRef</code> and this object's <code>ref</code> field is
   * set to that value.
   * Otherwise, this object's <code>ref</code> field is set to a
   * <code>RemoteRef</code> instance that is created of an
   * implementation-specific class corresponding to the external ref
   * type name returned by <code>readUTF</code>, and then
   * the <code>readExternal</code> method is invoked on
   * this object's <code>ref</code> field.
   *
   * <p>If the external ref type name is
   * <code>"UnicastRef"</code>, <code>"UnicastServerRef"</code>,
   * <code>"UnicastRef2"</code>, <code>"UnicastServerRef2"</code>,
   * or <code>"ActivatableRef"</code>, a corresponding
   * implementation-specific class must be found, and its
   * <code>readExternal</code> method must read the serial data
   * for that external ref type name as specified to be written
   * in the <b>serialData</b> documentation for this class.
   * If the external ref type name is any other string (of non-zero
   * length), a <code>ClassNotFoundException</code> will be thrown,
   * unless the implementation provides an implementation-specific
   * class corresponding to that external ref type name, in which
   * case this object's <code>ref</code> field will be set to an
   * instance of that implementation-specific class.
   */
  private void readObject(java.io.ObjectInputStream in)
      throws java.io.IOException, java.lang.ClassNotFoundException {
    String refClassName = in.readUTF();
    if (refClassName == null || refClassName.length() == 0) {
            /*
             * No reference class name specified, so construct
             * remote reference from its serialized form.
             */
      ref = (RemoteRef) in.readObject();
    } else {
            /*
             * Built-in reference class specified, so delegate to
             * internal reference class to initialize its fields from
             * its external form.
             */
      String internalRefClassName =
          RemoteRef.packagePrefix + "." + refClassName;
      Class<?> refClass = Class.forName(internalRefClassName);
      try {
        ref = (RemoteRef) refClass.newInstance();

                /*
                 * If this step fails, assume we found an internal
                 * class that is not meant to be a serializable ref
                 * type.
                 */
      } catch (InstantiationException e) {
        throw new ClassNotFoundException(internalRefClassName, e);
      } catch (IllegalAccessException e) {
        throw new ClassNotFoundException(internalRefClassName, e);
      } catch (ClassCastException e) {
        throw new ClassNotFoundException(internalRefClassName, e);
      }
      ref.readExternal(in);
    }
  }
}
